- 74 Downloads
Primates comprise an order within Mammalia and consist of prosimians, monkeys, and ape species.
Despite the popularity of the topic of human personality within Psychology, research into the personality of animals was discouraged until fairly recently in Psychology’s history. Even in modern times, the term “personality” has been eschewed in favor of terms such as “behavioral syndrome,” “behavioral type,” “temperament,” or “disposition.” Alternatively, researchers have simply referred to “individual differences.” This aversion to the idea of animal personalities likely owes a debt to the Cartesian notion that only humans had souls or were capable of emotion. Animals were likened to machines, and intraspecies variability was considered uninteresting relative to interspecies differences. In contrast, today, researchers are actively exploring the extent to which nonhumans exhibit stable and enduring characteristics akin to human personality traits (for two recent edited volumes devoted to this topic see Carere and Maestripieri 2013 and Vonk et al. under contract). An entire volume has been devoted solely to personality in nonhuman primates as well (Weiss et al. 2011b). Acknowledging such differences within species can help to guide animal welfare decisions in captive settings and to inform conservation efforts both in the wild and in captivity. The study of animal personality can also enhance understanding of differences in cognitive performance in psychological research with nonhumans.
Studies of Personality in Nonhuman Primates
References to unique dispositions of animal subjects appear in the writing of researchers long before the empirical study of temperament in nonhumans was deemed acceptable. For example, Kinnaman spoke of individual temperaments in his monkey subjects as far back as 1902. Better known work is that of Ivan Pavlov, who explicitly studied such topics as neuroses in his canine subjects. Pavlov recognized that dogs exhibited markedly distinct reactions to the same environmental stimuli, with dogs showing extreme reactivity being most likely to develop anxious and neurotic behaviors later, and more likely to forget conditioned responses (Pavlov 1966). These behavioral syndromes in dogs were likened to the human concept of Type A personality, but the concepts of passivity and extreme reactivity may also relate to Eysenck’s notion of introversion and extraversion. Pavlov was far ahead of his time in linking broad classes of behaviors to physiological components, for example, believing traits to arise as a function of the animal’s nervous system. Although not fully appreciated in its time, today’s researchers have found great value in such basic research. Temperament can now be used to predict an animal’s performance in roles such as service dogs, police dogs, animal demonstrators, and so on. Furthermore, researchers can use information about the genetic or physiological basis for such traits to aid in selective breeding or conservation programs. Enrichment items and even pet-owners can be matched to individuals based on their unique personalities. Thus, along with providing a deeper theoretical understanding of the evolution of personality in humans, the study of nonhuman personality has many practical applications.
The majority of the work on personality in nonhumans has focused on nonhuman primates, in particular, the closest living relatives to humans – chimpanzees. Crawford (1938) developed the first behavior rating scale that provided evidence of variable chimpanzee personalities. Crawford forecasted later debates in the field by voicing concern with the use of both rating scales and observations of specific behaviors by trained observers. These two techniques exemplify the methods of rating versus coding that are often used today in assessing nonhuman personality. Although both techniques require expertise, only the rating method requires the rater to be intimately familiar with the subjects. Of course, both methods rely on human observers and, thus, are subject to anthropomorphism and lack of objectivity.
Crawford’s early attempts to quantify individual differences in chimpanzees were followed by Hebb’s 1949 project, “Temperament in Chimpanzees.” Hebb, like Crawford, was interested in the consistency of behavior across time and contexts, such as feeding, but relied primarily on observation, rather than rating scales. Hebb identified broad categories of behaviors such as friendliness, aggression, avoidance, and unresponsiveness.
Later projects followed in the tradition of coding behavior across contexts, such as group interactions, exposure to infants, but added the use of factor analytic techniques to reduce the observed behaviors into factors. Chamove et al. (1972) found that factors of hostility, fear, and sociality emerged from such analyses. These factors appeared roughly analogous to the human personality factors of psychoticism, neuroticism-stability, and extraversion-introversion. Factor analysis was also applied to the rating scale approach of Crawford, in Stevenson-Hinde’s work with macaques (Stevenson-Hinde and Hinde 2011). Hinde’s work suggested two important factors; a confident to fearful dimension and an active to slow dimension. Later versions of her scale produced a third dimension of traits from sociable to solitary. These dimensions also align with the earlier work of Chamove et al. (1972). More recent work from Suomi’s lab (e.g., Suomi et al. 2011) has identified traits of fearfulness or anxiety, impulsivity, and more relaxed traits, which also appear somewhat analogous to a subset of human specific traits. Suomi and colleagues have extended the study of personality traits to identify influences of rearing and genetics on personality. In addition to clarifying the development of personality in nonhuman primates, such studies are crucial to understanding human personality. One reason for this is that experimental techniques that are not possible with humans can sometimes be applied to nonhumans. For example, infant primates can be cross fostered, which allows researchers to disentangle the influence of genetics and rearing environment on later personality development.
Conversely, data from humans can also inform the study of nonhuman personality. Because the study of human personality is farther along, researchers can also extend findings from techniques used only in humans, such as questionnaires, to seek similar factors in nonhuman personality structure. Although researchers have applied the five-factor model (e.g., introversion/extraversion, conscientiousness, neuroticism, openness, agreeableness) to nonhuman primates, these studies have failed to confirm the presence of the same five factors and have also often indicated an additional factor. This sixth factor is sometimes identified as dominance, which appears to be extremely important for describing variability in chimpanzee behavior (King and Figueredo 1997). Since this key publication, the study of animal personality has virtually exploded and it is likely that the human conception of nonhuman primate personality will continue to evolve over the next several decades. Freeman et al. (2013) also identified six factors to describe chimpanzee personality, but their sixth factor was tentatively labeled, “Methodical” and awaits further data. This factor includes, in addition to methodical itself, intelligence and self-caring. Freeman et al. identified the challenges of both “top-down” approaches that apply ideas about traits previously identified in other species to the species in question, with “bottom-up” approaches that derive traits specifically for the species in question, but may hinder comparisons to other species. Other approaches, such as the circumplex model of human personality, have not yet been applied to nonhuman primates, but should prove to be a fruitful approach (see Zeigler-Hill and Highfill in press). A circumplex model might examine where individuals fall along a continuum of complimentary traits such as dominance/subordination and affiliation/aggression.
Because this is a bourgeoning area of research, the current state of knowledge should be viewed as preliminary. Although there are some basic similarities between the personality of humans and other apes that cannot be attributed to anthropocentric biases (Weiss et al. 2012), Weiss et al. (2011a) have also shown that a single general factor of personality does not appear to be shared between chimpanzees, orangutans, and rhesus macaques, suggesting the need to study each species separately. Some authors have also argued for four, rather than five- or six-factor solutions, and it is not yet clear how neatly the factors derived from studies of nonhumans map onto the traits validated in human samples. What can be conclusively determined, however, is that nonhuman primates show as much variability as their human counterparts and can no longer be considered machine-like counterparts to humans.
- Freeman, H. D., Brosnan, S. F., Hopper, L. M., Lambeth, S. P., Schapiro, S. J., & Gosling, S. D. (2013). Developing a comprehensive and comparative questionnaire for measuring personality in chimpanzees using a simultaneous top-down/bottom-up design. American Journal of Primatology, 75, 1042–1053.CrossRefPubMedGoogle Scholar
- Pavlov, I. (1966). Constitutional differences and functional disturbances: Experimental neuroses. In M. Kaplan (Ed.), Essential works of Pavlov (pp. 261–267). New York: Bantam Books.Google Scholar
- Vonk, J., Weiss, A., & Kuczaj, S. (under contract). Personality in non-human animals. Springer. New York.Google Scholar
- Weiss, A., Adams, M. J., & Johnson, W. (2011a). The big none: No evidence for a general factor of personality in chimpanzees, orangutans, or rhesus macaques. Journal of Research in Personality, 45, 393–397.Google Scholar
- Weiss, A, King, E. J., & Murray, L. (Eds.). (2011b). Personality and temperament in nonhuman primates (pp. 3–14). New York: Springer New York.Google Scholar
- Zeigler-Hill, V., & Highfill, L. (in press). The interpersonal circumplex: A complementary approach for studying animal personality. In J. Vonk, A. Weiss, & S. Kuzjac (Eds.), Personality in non-humans. New York: Springer.Google Scholar